1. Field of the Invention
The present invention relates to a technology for attaining stable operation of a charge pump-type DC/DC converter.
2. Description of the Related Art
A multi-output charge pump-type DC/DC converter is known, as disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2005-278356, for example. This kind of charge pump-type DC/DC converter has a structure in which a plurality of stages of charge pumps is connected in series.
The conventional charge pump-type DC/DC converter generates a driving signal of the first stage charge pump by shifting the level of the power-supply voltage VDD by the output voltage of the first stage charge pump.
However, a problem has often occurred in the conventional charge pump-type DC/DC converter whereby the output voltage (initial value) of the first stage charge pump does not rise to the operating voltage of a level shifter when building up the DC/DC converter due to a parasitic diode of a transistor within the charge pump, thus generating no driving signal. This problem is particularly pronounced when the voltage (reference voltage) that is the basis of boosting is low.
Accordingly, a charge pump-type DC/DC converter that steadily operates even when the reference voltage is low is required.